Optical pick-up apparatus

ABSTRACT

The present invention provides a method and apparatus for utilizing light rays of differing wavelengths to read optical discs of different respective capacities. The present invention serves to prevent aberration of the minute optical spot used to read the respective optical discs and also serves to eliminate an offset component with respect to the signals received by the photo detector, as reflected from the respective optical discs.

[0001] The present invention is based upon and claims priority fromJapanese Patent Application No. 10-102827 filed on Apr. 14, 1998, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an optical pick-up apparatuswith two light sources. More specifically, the present invention relatesto an optical pick-up apparatus capable of utilizing two respectivelight sources, each having a different wavelength, for reading tworespective types of optical discs, and wherein, no photo detectoradjustment is required in order to read each type of disk.

[0004] 2. Description of the Related Art

[0005]FIG. 5 shows the general structure of a conventional opticalpick-up apparatus. A light ray radiating from a laser diode 11 iscollimated by a collimator lens 12 and its beam form is shaped by a beamshaping prism 13. It passes through a beam splitter 14 and is deflected90 degrees by a deflective prism 15. It is then focused by an objectivelens 16 and radiated on an optical disc 17 as a minute optical spot.Recording, reproducing and erasing information on the optical disc 17are carried out by this optical spot.

[0006] A light ray reflected off of the optical disc 17 is collimated bythe objective lens 16 again, and its path is deflected 90 degrees by thedeflective prism 15. It is reflected by the beam splitter 14 and isfocused by a focusing lens 18. Cylindrical lens 19 provides astigmatismand the light ray is received on photo detector 20. It is photo detector20 that detects the information signal and the servo signal as usedwithin the optical pick-up apparatus.

[0007] Recent attempts to increase optical disc capacity have led to thepractice of shortening the wavelength of the light source used to readthese higher capacity discs. In general, the illuminated spot radial onan optical disc is proportional to the wavelength λ of the light sourceused to read the disc, and the capacity of the optical disc is inverselyproportional to the square of the wavelength λ. Notwithstanding thetrend toward using shorter wavelengths, there do exist optical discdrives that depend on the longer wavelengths. For example, the discdrive might depend on a reflective rate of the optical disc and also onthe recording power. In such instances, it is impossible to reproduceand record information on a conventional disc by using a light sourcewith a shortened wavelength.

[0008] Accordingly, for the purpose of establishing compatibilitybetween conventional discs and optical discs has larger capacities, anoptical disc drive might have two different kinds of light sources. Onelight source has a short wavelength (e.g., 650 nm), the other lightsource has a conventional wavelength (e.g., 785 nm). The simplest way torealize such a combined disc drive is to employ two separate pick-upapparatuses, each of which employs a light source having a differentwavelength. However, in this case, such a drive would become too largeand too expensive to be practical.

[0009] On the other hand, both the size and cost of such a combinedarrangement could be reduced if two separate light sources, each havinga different wavelength, could be processed using one common opticalarrangement.

[0010]FIG. 6 shows such a conventional optical pick-up apparatus. Theoptical parts depicted in FIG. 6 are common to those optical partsdepicted within the optical pick-up device of FIG. 5, the onlydifference being the light source 21. For example, a first light sourcecomprising a laser diode (LD) chip having a wavelength of 650 nm and asecond light source comprising a laserdiode (LD) chip having awavelength of 785 nm are separated by a very small distance which rangesfrom scores to hundreds of nanometers (nm). One light source, in thelight source portion 21, is located on the optical axis of thecollimator lens 12, a ray from this light source travels as a solid lineof FIG. 6. The other light source, in the light source portion 21, islocated such that it is slightly departed from the optical axis of thecollimator lens 12, a ray from this light source travels as a dottedline of FIG. 6. These two light sources are used selectively.

[0011] For example, an optical information recording and reproducingapparatus, as disclosed in Japanese unexamined patent (KOKAI) No.06-259804, comprises a first light source, a second light source, anoptical beam composing means for composing rays from respective lightsources on the same optical path, an optical arrangement which makes abeam from the first light source focused on the first optical disc andmakes a beam from the second light source focused on the second opticaldisc, and photo detectors for receiving reflective rays from both thefirst optical disc and the second optical disc.

[0012] In the FIG. 6 optical pick-up apparatus, one light source, in thelight source portion 21, is located on the optical axis of thecollimator lens 12, the other light source in the light source portion21, is located such that it is slightly departed from the optical axisof the collimator lens 12. A light ray radiating from the collimatorlens 12, which is departed from its optical axis, is incident to theinclining of that light ray from the objective lens. Furthermore, sinceaberration occurs and it is difficult to form a good optical illuminatedspot on the optical disc 17, and also, since two rays having differentwavelengths reflected on the optical disc are incident to the converginglens 18 with different angles, the incident respective positions of thereflected light rays on the photo detector 20 are different. Therefore,when adjustments are made to the photo detector 20 for a light rayhaving one wavelength, a servo signal detected by the photo detector fora ray having a different wavelength necessarily has an offset component.

[0013] Thus, there exists a need for an apparatus and method whichallows for the use of a single optical arrangement for utilizing lightrays of differing wavelengths to read optical discs of differentrespective capacities, and wherein optical signals received by the photodetector as reflected from the respective optical discs do not containan offset component.

SUMMARY OF THE INVENTION

[0014] The present invention overcomes the problems associated with theprior art and provides a method and apparatus for utilizing light raysof differing wavelengths to read optical discs of different respectivecapacities. The present invention serves to prevent aberration of theminute optical spot used to read the respective optical discs and alsoserves to eliminate an offset component with respect to the signalsreceived by the photo detector, as reflected from the respective opticaldiscs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] These and other advantages and features of the invention will bemore clearly understood from the following detailed description of theinvention which is provided in connection with the accompanying drawingsin which:

[0016]FIG. 1 depicts a first optical arrangement of the invention;

[0017]FIG. 2 depicts a portion of a second optical arrangement of theinvention;

[0018]FIG. 3 depicts a portion of the FIG. 1 arrangement in more detail;

[0019]FIG. 4 depicts a portion of a third optical arrangement of theinvention;

[0020]FIG. 5 depicts a conventional optical pick-up apparatus; and

[0021]FIG. 6 depicts a conventional optical pick-up apparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0022] Preferred embodiments of the present invention will now bedescribed with reference to FIGS. 1-4. Other embodiments may be realizedand structural or logical changes may be made to the disclosedembodiments without departing from the spirit or scope of the presentinvention.

[0023]FIG. 1 depicts a first optical arrangement of the invention. Therefractive index of optical glass, for a given light ray passing throughit, varies with the wavelength of the light ray, and in general, if thelight's wavelength is greater, the refractive index of the optical glassis lower.

[0024] As shown in FIG. 3, two light sources 32, 33, having respectivewavelengths λ1 and λ2, are located such that θ1>θ2, where an angle inwhich the light of wavelength λ1, from the first light source 32, isincident to the beam shaping prism 31 is θ1, and an angle in which thelight of wavelength λ2, from the second light source 33, is incident tothe beam shaping prism 31 is θ2. In accordance with the presentinvention, a light with wavelength λ1 and a light with wavelength λ2(λ1<λ2) can be shaped by the beam shaping prism 31, wherein the angleswith which the lights are radiated from the beam shaping prism 31 arenearly equal.

[0025] As depicted in FIG. 1, light rays from two separate light sources32, 33 are composed by beam composing means 34 (e.g., a dichroic prism).Light from the prism 34 is then collimated by the collimator lens 35 andits beam form is shaped by the beam shaping prism 31. Upon leaving beamshaping prism 31, the light rays are radiated in nearly equal angles.The light rays then pass through the beam splitter 36 and then theirpath is deflected 90 degrees by the deflective prism 37 where the lightis then radiated on the optical disc 39 as a minute optical spot thathas been focused by the object lens 38. Recording, reproducing anderasing of information on the optical disc is carried out by the opticalspot.

[0026] A reflective light from the optical disc 39 is collimated by theobjective lens 38 and is again deflected 90 degrees by the deflectiveprism 37. The light is then reflected by the beam splitter 36 and isconverged by the converging lens 40. Cylindrical lens 41 providesastigmatism and the light is then received by photo detector 42. Aninformation signal and a servo signal are detected by the photo detector42 for use within the optical pick-up apparatus.

[0027] In accordance with the present invention, the particular opticaldisc which is being read determines which light source (32 or 33) isactive. For example, for the first optical disc, a first light source 32is active and light source 33 is inactive. Similarly, for the secondoptical disc, a second light source 33 is active and light source 32 isinactive.

[0028] Still referring to FIG. 1, a pick-up apparatus is depicted inaccordance with a first embodiment of the present invention. The pick-upapparatus has a first light source 32 which radiates a light ofwavelength λ1, and a second light source 33 which radiates a light ofwavelength λ2, where λ2 is greater than λ1. Light from each source 32,33 then passes through composing means 34 (e.g., a dichroic prism) wherethe light rays are composed. Next, the light rays pass through acollimate lens 35 which collimates the lights from each respectivesource 32, 33. The lights then pass through a beam shaping prism 31which shapes an optical beam form from the collimator lens 35. Anobjective lens 38 is employed for focussing light from the beam shapingprism 31 onto the optical disc 39. A photo detector 42 detects aninformation signal and servo signals by receiving light reflected fromthe optical disc 39.

[0029] The FIG. 1 pick-up apparatus focuses light from the first lightsource 32 on a first optical disc, and focuses light from the secondlight source 32 on a second optical disc, wherein the substratethickness of the second optical disc differs from that of the firstoptical disc. As an angle in which light from the second light source 33is incident to the beam shaping prism 31 is smaller than an angle inwhich light from the first light source 32 is incident to the beamshaping prism 31, the first light source 32 and the second light source33 are located. Therefore, it is possible to make radiant angles of thebeam shaping prism 31 for lights of the two different wavelengths λ1, λ2nearly equal. Furthermore, an incident angle of the objective lens 38for lights of the two different wavelengths λ1, λ2 is small, therebyreducing aberration of the optical spot for lights of the two differentwavelengths λ1, λ2.

[0030] Turning now to FIG. 2, the portion of a second opticalarrangement of the invention is depicted. In FIG. 2 embodiment, a singlelight source portion 43, having two laser diode chips in the samepackage is used, thereby eliminating a need for composing means 34. Thetwo LD chips in this light source portion 43 comprise a first LD chipradiating a light of wavelength λ1 and a second LD chip radiating alight of wavelength λ2.

[0031] Lights of wavelength λ1, λ2 radiated from the two LD chips in thelight source portion 43 are collimated by the collimate lens 35, and areshaped by the beam shaping prism 31. As can be seen in FIG. 3, an anglein which the light of wavelength λ1, from the first light source 32, isincident to the beam shaping prism 31 is θ1. Similarly, an angle inwhich the light of wavelength λ2, from the second light source 33, isincident to the beam shaping prism 31 is θ2. As long as θ1>θ2, the twoLD chips, located within the same light source portion 43, canrespectively produce a light with wavelength λ1 and a light withwavelength λ2 (where λ<λ2), wherein the two separate lights can beshaped by the beam shaping prism 31 such that respective angles radiatedfrom the beam shaping prism 31 for both lights are nearly equal.

[0032] Defining an incident angle of the beam shaping prism 31 as θ0, arefractive index of material of the beam shaping prism 31 as n1 forwavelength λ1 light, and n2 for wavelength λ2 light, a focus distance ofthe collimator lens 35 as fc1, the distance between two LD chips in thelight source portion 43 is L. Utilizing the above definitions, anoptical arrangement of an embodiment of the invention is satisfied withthe following expression:

L=fc1×tan (arcsin (n1×sin θ0))−(arcsin (n2×sin θ0)).

[0033] Therefore, radiating angles of the lights of two wavelengths λ1,λ2 are equal.

[0034] For example, where θ0=32 degrees, fc1=8, material of the beamshaping prism 31 is SF11, λ1=650 nm, and λ2=785 nm, n1 is 1.776653 andn2 is 1.765743, L=0.13 mm. That is, if the two LD chips in the lightsource portion 43 are located 0.13 mm apart, incident angles of thelight of the two wavelengths λ1, λ2 for the objective lens 38 are nearlyequal.

[0035] Still referring to FIG. 2, a second embodiment puts the firstlight source and the second light source in the same package. The firstlight source 32 and the second light source 33 are located in the lightsource portion 43. As long as an angle in which a light from the secondlight source 33 is incident to the beam shaping prism 31 is smaller thanan angle in which a light from the first light source 32 is incident tothe beam shaping prism 31, it is possible to make a radiant angle of thebeam shaping prism for lights of the two wavelengths λ1, λ2 equal.Furthermore, incident angles of the objective lens for lights of the twowavelengths λ1, λ2 can be small and aberration of the minute opticalspot for lights of the two wavelengths λ1, λ2 is reduced.

[0036] Turning now to FIG. 4, a portion of a third optical arrangementof the invention is depicted. The FIG. 4 embodiment puts two lightsources 44, 45 and a photo detector 46 in the same package 47. Ahologram laser unit 49 comprises hologram 48 as a diffraction grating,wherein the hologram 48 is coupled to the package 47. As depicted inFIG. 4, the light source 43, the beam splitter 36, the focusing lens 40,the cylindorical lens 41 and the photo detector 42 are omitted.

[0037] A light radiated from one of the two light sources 44, 45 in thehologram laser unit 49 passes through the hologram 48 and is collimatedby the collimator lens 35. The beam form is shaped by the beam shapingprism 31 and its path is deflected 90 degrees by the deflective prism37. The light is then focused by the object lens 38 and is radiated onthe optical disc 39 as a minute optical spot. Recording, reproducing anderasing are carried out by the optical spot.

[0038] A reflective light from the optical disc 39 is the collimated bythe objective lens 38 at which point, the optical path is deflected 90degrees by the deflective prism 37. The light then passes through thebeam shaping prism 31 and the collimator lens 35, and is diffracted bythe hologram 48. Therefore, such optical path is separated from theradiating light path and is incident to the photo detector 46. Aninformation signal and a servo signal are detected by photo detector 46.Therefore, it is possible to form a good optical spot on an optical discwhile miniaturizing a drive by reducing the number of parts used in thedisc drive. A cost savings is also realized through the incorporation ofthe present invention.

[0039] As is apparent from FIGS. 1 and 4, incident angles of the lightsof wavelengths λ1, λ2 for the objective lens 38 can be zero degrees,however, incident angles of the lights of wavelengths λ1, λ2 for thecollimator lens 35 cannot be zero degrees. Therefore, in eachembodiment, one of the two light sources which radiates a shortwavelength λ1 light for reproducing, recording and erasing informationon a high density optical disc is located on the optical axis of thecollimator lens 35. Therefore, it is possible to make the shortwavelength λ1 light be incident to the collimator lens 35 and theobjective lens 38 in an ideal condition, thereby allowing for theforming of a good optical spot on the optical disc.

[0040] On the other hand, the long wavelength λ2 light is incident tothe collimator lens 35 with inclination. In accordance with the presentinvention, the inclination of the incident angle for the long wavelengthλ2 light to the collimator lens does not pose a problem because apermitted level of incident angle error of the long wavelength λ2 lightfor the collimator lens is greater than that of the incident angle errorof the short wavelength λ1 light for the object lens. Therefore, themargin for aberration of the optical spot for purposes of reproducing,recording and erasing information is greater.

[0041] While preferred embodiments of the invention have been describedand illustrated, it should be apparent that many modifications can bemade to the invention without departing from its spirit or scope. Forexample, while specific exemplary wavelengths have been discussed inconnection with preferred embodiments of the present invention, theinvention may be employed for use with light rays having wavelengthsdifferent than those depicted herein. Accordingly, the invention is notlimited by the foregoing description or drawings, but is only limited bythe scope of the appended claims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A system for use with optical diskreproduction, the system comprising: a plurality of light sources, afirst one of said plurality of light sources being capable of producinglight rays of a first wavelength, a second one of said plurality oflight sources being capable of producing light rays of a secondwavelength, said second wavelength being greater than said firstwavelength; beam composing means, said beam composing means beinglocated such that it is capable of alternatively passing light raysreceived from each of at least said first and second light sources fromrespective light entry portions of said beam composing means to a lightexiting portion of said beam composing means, wherein said first andsecond light rays exit said beam composing means in respective exitangles such that they would converge at a convergence point located at apredetermined distance from said beam composing means; and a beamshaping prism, a light entry portion of said beam shaping prism beinglocated at said convergence point, wherein an angle with which saidlight rays of said first wavelength are incident to said beam shapingprism is greater than an angle with which said light rays of said secondwavelength are incident to said beam shaping prism and wherein,respective angles of said first and second light rays are nearly equalupon said light rays exiting said beam shaping prism.
 2. The system asin claim 1 further comprising a collimator lens located between saidbeam composing means and said beam shaping prism for collimating saidfirst and second light rays before said light rays enter said beamshaping prism.
 3. The system as in claim 1 further comprising a beamsplitter located such that said first and second light rays enter alight entry portion of said beam splitter upon exiting said beam shapingprism.
 4. The system as in claim 3 further comprising a deflective prismfor deflecting a path of said first and second light rays, saiddeflective prism being located such that said first and second lightrays are deflected upon exiting said beam splitter.
 5. The system as inclaim 4, wherein said deflective prism is capable of deflecting a pathof said first and second light rays by 90 degrees.
 6. The system as inclaim 4 further comprising an optical disc from which said first andsecond light rays are reflected after said light rays have beendeflected by said deflective prism.
 7. The system as in claim 6 furthercomprising an object lens for focusing said first and second light raysonto said optical disc after they have been deflected by said deflectiveprism.
 8. The system as in claim 6 further comprising a photo detectorfor detecting an information signal and servo signals by receiving saidfirst and second light rays as reflected from said optical disc.
 9. Thesystem as in claim 8 further comprising a cylindrical lens for providingastigmatism of said first and second reflected light rays before saidreflected light rays are received by said photo detector.
 10. The systemas in claim 9, wherein said first and second reflected light rays arereflected by said beam splitter before said reflected light rays arereceived by said cylindrical lens.
 11. The system as in claim 10 furthercomprising a convergent lens for converging said first and secondreflected light rays before said reflected light rays are received bysaid cylindrical lens.
 12. The system as in claim 10, wherein said firstand second reflected light rays are deflected by said deflective prismbefore said reflected light rays are reflected by said beam splitter.13. The system as in claim 12, wherein said deflective prism deflects apath of said first and second reflected light rays by 90 degrees. 14.The system as in claim 12, wherein said first and second reflected lightrays are collimated by said objective lens before said reflected lightrays are deflected by said deflective prism.
 15. The system as in claim1, wherein said beam composing means comprises a dichroic prism.
 16. Thesystem as in claim 1, wherein said light sources further comprise laserdiodes.
 17. The system as in claim 1, wherein said first wavelength isapproximately 650 nm.
 18. The system as in claim 1, wherein said secondwavelength is approximately 785 nm.
 19. The system as in claim 2,wherein said first light rays are passed through an optical axis of saidcollimator lens.
 20. A system for use with optical disk reproduction,the system comprising: a plurality of light sources, a first one of saidplurality of light sources being capable of producing light rays of afirst wavelength, a second one of said plurality of light sources beingspatially separated from said first light source by a predetermineddistance, said second light source also being capable of producing lightrays of a second wavelength, said second wavelength being greater thansaid first wavelength, wherein said first and second light sources arelocated such that said first and second light rays converge at aconvergence point located at a predetermined distance from each of saidfirst and second light sources; and a beam shaping prism, a light entryportion of said beam shaping prism being located at a predetermineddistance beyond said convergence point for alternatively passing lightrays received from each of said first and second light sources from saidlight entry portion to a light exiting portion of said beam shapingprism, wherein an angle with which said light rays of said firstwavelength are incident to said beam shaping prism is greater than anangle with which said light rays of said second wavelength are incidentto said beam shaping prism, and wherein respective angles of said firstand second light rays are nearly equal upon said light rays exiting saidbeam shaping prism.
 21. The system as in claim 20, wherein said firstand second light sources are coupled within a common package.
 22. Thesystem as in claim 20, further comprising a collimator lens forcollimating said first and second light rays, a light entry portion ofsaid collimator lens being located at said convergence point.
 23. Thesystem as in claim 22, wherein said predetermined distance whichspatially separates said first and second light sources is defined bythe expression: L=fc1×tan (arcsin (n1×sin θ0))−(arcsin (n2×sin θ0)),wherein L is the distance in mm, θ0 is an incident angle of said beamshaping prism, n1 and n2 are respective refractive indices of a materialof said beam shaping prism for said first and second light sources, andfc1 is a focus distance of said collimator lens.
 24. The system as inclaim 20 further comprising a beam splitter located such that said firstand second light rays enter a light entry portion of said beam splitterupon exiting said beam shaping prism.
 25. The system as in claim 24further comprising a deflective prism for deflecting a path of saidfirst and second light rays, said deflecting prism being located suchthat said first and second light rays are deflected upon exiting saidbeam splitter.
 26. The system as in claim 25, wherein said deflectiveprism is capable of deflecting a path of said first and second lightrays by 90 degrees.
 27. The system as in claim 24 further comprising anoptical disc from which said first and second light rays are reflectedafter said light rays have been deflected by said deflective prism. 28.The system as in claim 27 further comprising an object lens for focusingsaid first and second light rays onto said optical disc after they havebeen deflected by said deflective prism.
 29. The system as in claim 27further comprising a photo detector for detecting an information signaland servo signals by receiving said first and second light rays asreflected from said optical disc.
 30. The system as in claim 27 furthercomprising a cylindrical lens for providing astigmatism of said firstand second reflected light rays before said reflected light rays arereceived by said photo detector.
 31. The system as in claim 30, whereinsaid first and second reflected light rays are reflected by said beamsplitter before said reflected light rays are received by saidcylindrical lens.
 32. The system as in claim 31 further comprising aconvergent lens for converging said first and second reflected lightrays before said reflected light rays are received by said cylindricallens.
 33. The system as in claim 31, wherein said first and secondreflected light rays are deflected by said deflective prism before saidreflected light rays are reflected by said beam splitter.
 34. The systemas in claim 33, wherein said deflective prism deflects a path of saidfirst and second reflected light rays by 90 degrees.
 35. The system asin claim 33, wherein said first and second reflected light rays arecollimated by said objective lens before said reflected light rays aredeflected by said deflective prism.
 36. The system as in claim 20,wherein said light sources further comprise laser diodes.
 37. The systemas in claim 20, wherein said first wavelength is approximately 650 nm.38. The system as in claim 20, wherein said second wavelength isapproximately 785 nm.
 39. The system as in claim 22, wherein said firstlight rays are passed through an optical axis of said collimator lens.40. A system for use with optical disc reproduction, the systemcomprising: a plurality of light sources, a first one of said pluralityof light sources being capable of producing light rays of a firstwavelength, a second one of said plurality of light sources beingspatially separated from said first light source by a predetermineddistance, said second light source also being capable of producing lightrays of a second wavelength, said second wavelength being greater thansaid first wavelength, wherein said first and second light sources arelocated such that said first and second light rays converge at aconvergence point located at a predetermined distance from each of saidfirst and second light sources; and a beam shaping prism, a light entryportion of said beam shaping prism being located at said convergencepoint for alternatively passing light rays received from each of saidfirst and second light sources from said light entry portion to a lightexiting portion of said beam shaping prism, wherein an angle with whichsaid light rays of said first wavelength are incident to said beamshaping prism is greater than an angle with which said light rays ofsaid second wavelength are incident to said beam shaping prism, andwherein respective angles of said first and second light rays are nearlyequal upon said light rays exiting said beam shaping prism.
 41. Thesystem as in claim 40 further comprising a collimator lens locatedbetween said plurality of light sources and said beam shaping prism forcollimating said first and second light rays before said light raysenter said beam shaping prism.
 42. The system as in claim 40 furthercomprising a deflective prism for deflecting a path of said first andsecond light rays, said deflective prism being located such that saidfirst and second light rays are deflected upon exiting said beam shapingprism.
 43. The system as in claim 42, wherein said deflective prism iscapable of deflecting a path of said first and second light rays by 90degrees.
 44. The system as in claim 42 further comprising an opticaldisc from which said first and second light rays are reflected aftersaid light rays have been deflected by said deflective prism.
 45. Thesystem as in claim 44 further comprising a photo detector for detectingan information signal and servo signals by receiving said first andsecond light rays as reflected from said optical disc, said photodetector and said first and second light sources being coupled within acommon package.
 46. The system as in claim 45 further comprising adiffraction grating for modifying a light path of said first and secondlight rays before said first and second light rays are received by saidphoto detector, said diffraction grating being located between saidoptical disc and said photo detector.
 47. The system as in claim 46,wherein said diffraction grating comprises a hologram.
 48. The system asin claim 41, wherein said first light rays are passed through an opticalaxis of said collimator lens.
 49. A method of reproducing an opticaldisc, the method comprising: receiving light rays from a plurality oflight sources at a beam composing means, a first one of said pluralityof light sources producing light rays of a first wavelength, a secondone of said plurality of light sources producing light rays of a secondwavelength, said second wavelength being greater than said firstwavelength; passing said light rays from said first and second lightsources from respective light entry portions of said beam composingmeans to a light exiting portion of said beam composing means, whereinsaid first and second light rays exit said beam composing means inrespective angles such that they converge at a convergence point locatedat a predetermined distance from said beam composing means; and passingsaid first and second light rays through a beam shaping prism, a lightentry portion of said beam shaping prism being located at saidconvergence point, wherein an angle with which said light rays of saidfirst wavelength are incident to said beam shaping prism is greater thanan angle with which said light rays of said second wavelength areincident to said beam shaping prism, and wherein respective angles ofsaid first and second light rays are nearly equal upon said light raysexiting said beam shaping means.
 50. The method as in claim 49 furthercomprising collimating said first and second light rays upon exitingsaid beam composing means and before said light rays enter said beamshaping prism.
 51. The method as in claim 49 further comprising passingsaid first and second light rays through a beam splitter upon said raysexiting said beam shaping prism.
 52. The method as in claim 51 furthercomprising deflecting a path of said first and second light rays into adirection of an optical disc.
 53. The method as in claim 52 furthercomprising reflecting one of said first and second light rays off ofsaid optical disc.
 54. The method as in claim 53 further comprisingfocusing said first and second light rays onto said optical disc aftersaid first and second light rays have been deflected.
 55. The method asin claim 53 further comprising receiving said reflected light rays at aphoto detector.
 56. The method as in claim 55 further comprisingproviding astigmatism of said reflected light rays before said reflectedlight rays are received at said photo detector.
 57. The method as inclaim 56 further comprising reflecting said reflected light rays off ofsaid beam splitter before said reflected light rays are provided withastigmatism.
 58. The method as in claim 57 further comprising convergingsaid reflected light rays before said reflected light rays are providedwith astigmatism.
 59. The method as in claim 57 further comprisingdeflecting a path of said reflected light rays before said reflectedlight rays are reflected by said beam splitter.
 60. The method as inclaim 59 further comprising collimating said reflected light rays beforesaid reflected light rays are deflected.
 61. The method as in claim 50,wherein said act of collimating further comprises passing said firstlight rays through an optical axis of a collimator lens.
 62. A method ofreproducing an optical disc, the method comprising: emitting light raysfrom a plurality of light sources in a direction of a beam shapingprism, a first one of said plurality of light sources producing lightrays of a first wavelength, a second one of said plurality of lightsources producing light rays of a second wavelength, said secondwavelength being greater than said first wavelength, wherein said firstand second light sources are located such that light rays of said firstwavelength and light rays of said second wavelength converge at aconvergence point located at a predetermined distance from each of saidfirst and second light sources; receiving said first and second lightrays at said beam shaping prism, a light entry portion of said beamshaping prism being located at a predetermined distance beyond saidconvergence point, wherein an angle with which said light rays of saidfirst wavelength are incident to said beam shaping prism is greater thanan angle with which said light rays of said second wavelength areincident to said beam shaping prism; and passing said first and secondlight rays from said light entry portion to a light exiting portion ofsaid beam shaping prism, wherein respective angles of said first andsecond light rays are nearly equal upon said light rays exiting saidbeam shaping prism.
 63. The method as in claim 62 further comprisingcollimating said first and second light rays before said light rays arereceived by said beam shaping prism.
 64. The method as in claim 63,wherein said act of emitting further comprises emitting light rays froma plurality of light sources, at least said first and second lightsources being coupled to a common package, wherein said first and secondlight sources are spatially separated by distance L, where L is definedby the expression L=fc1×tan (arcsin (n1×sin θ0))−(arcsin (n2×sin θ0)),and wherein L is the spatial separation in mm, θ0 is a incident angle ofsaid beam shaping prism, n1 and n2 are respective refractive indices ofa material of said beam shaping prism for said first and second lightrays, and fc1 is a focus distance of a lens used for said act ofcollimating.
 65. The method as in claim 62 further comprising passingsaid first and second light rays through a beam splitter upon said raysexiting said beam shaping prism.
 66. The method as in claim 65 furthercomprising deflecting a path of said first and second light rays into adirection of an optical disc.
 67. The method is in claim 66 furthercomprising reflecting one of said first and second light rays off ofsaid optical disc.
 68. The method as in claim 67 further comprisingfocusing said first and second light rays onto said optical disc aftersaid first and second light rays have been deflected.
 69. The method asin claim 67 further comprising receiving said reflected light rays at aphoto detector.
 70. The method as in claim 69 further comprisingproviding astigmatism of said reflected light rays before said reflectedlight rays are received at said photo detector.
 71. The method as inclaim 70 further comprising reflecting said reflected light rays off ofsaid beam splitter before said reflected light rays are provided withastigmatism.
 72. The method as in claim 71 further comprising convergingsaid reflected light rays before said reflected light rays are providedwith astigmatism.
 73. The method as in claim 71 further comprisingdeflecting a path of said reflected light rays before said reflectedlight rays are reflected by said beam splitter.
 74. The method as inclaim 73 further comprising collimating said reflected light rays beforesaid reflected light rays are deflected.
 75. The method as in claim 63,wherein said act of collimating further comprises passing said firstlight rays through an optical axis of a collimator lens.
 76. A method ofreproducing an optical disc, the method comprising: emitting light raysfrom a plurality of light sources in a direction of a beam shapingprism, a first one of said plurality of light sources producing lightrays of a first wavelength, a second one of said plurality of lightsources producing light rays of a second wavelength, said secondwavelength being greater than said first wavelength, wherein said firstand second light sources are located such that light rays of said firstwavelength and light rays of said second wavelength converge at aconvergence point located at a predetermined distance from each of saidfirst and second light sources; receiving said first and second lightrays at said beam shaping prism, a light entry portion of said beamshaping prism being located at said convergence point, wherein an anglewith which said light rays of said first wavelength are incident to saidbeam shaping prism is greater than an angle with which said light raysof said second wavelength are incident to said beam shaping prism; andpassing said first and second light rays from said light entry portionto a light exiting portion of said beam shaping prism, whereinrespective angles of said first and second light rays are nearly equalupon said light rays exiting said beam shaping prism.
 77. The method asin claim 76 further comprising collimating said first and second lightrays before said light rays are received by said beam shaping prism. 78.The method as in claim 76 further comprising deflecting a path of saidfirst and second light rays into a direction of an optical disc.
 79. Themethod as in claim 78 further comprising reflecting one of said firstand second light rays off of said optical disc.
 80. The method as inclaim 79 further comprising receiving said reflected light rays at aphoto detector.
 81. The method as in claim 80 further comprisingmodifying a light path of said reflected light rays with a diffractiongrating before said reflected light rays are received by said photodetector.
 82. The method as in claim 81, wherein said act of modifyingcomprises modifying said light path with a hologram.
 83. The method asin claim 77, wherein said act of collimating further comprises passingsaid first light rays through an optical axis of a collimator lens.